Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that most often occurs in children, but can also be diagnosed in adulthood. Symptoms of ADHD include:

having trouble concentrating or focusing

having difficulty staying organized

being forgetful about completing tasks

having difficulty sitting still

It can be a difficult condition to diagnose. Many symptoms of ADHD can be typical childhood behaviors, so it can be hard to know what’s ADHD-related and what’s not. Here are the basic facts and symptoms of ADHD.

There are demographic factors that impact the risks of being diagnosed with ADHD. Children living in households where English is the main language are more than four times as likely to be diagnosed as children living in households where English is the second language. And children living in households that make less than two times the federal poverty level have a higher risk than children from higher-income households.

Certain conditions might affect certain races in different ways, but ADHD impacts children of all races. From 2001 to 2010, the rate of ADHD among non-Hispanic black girls increased over 90 percent.

Children are also diagnosed at different ages. Detecting symptoms differs from case to case, and the more severe the symptoms, the earlier the diagnosis.

8 years old: average age of diagnosis for children with mild ADHD

7 years old: average age of diagnosis for children with moderate ADHD

5 years old: average age of diagnosis for children with severe ADHD

On the rise

Cases and diagnoses of ADHD have been increasing dramatically in the past several years. The American Psychiatric Association (APA) says that 5 percent of American children have ADHD. But the Centers for Disease Control and Prevention (CDC) puts the number at more than double that. The CDC says that 11 percent of American children, ages 4 to 17, had the attention disorder as of 2011. That’s an increase of 42 percent between 2003 and 2011.

Increase in diagnoses:

2003: 7.8%

2007: 9.5%

2011: 11%

50 states

An estimated 6.4 million American children ages 4 to 17 have been diagnosed with ADHD. The incidence of ADHD is higher in some states than others.

Generally, states in the western parts of the United States have the lowest rates of ADHD. Nevada has the lowest rates. States in the Midwest seem to have the highest rates. Kentucky has the highest rates.

ADHD doesn’t increase a person’s risk for other conditions or diseases. But some people with ADHD — especially children — are more likely to experience a range of coexisting conditions. They can sometimes make social situations more difficult or school more challenging.

Cost is a major factor when it comes to how a condition affects someone. Treatment plans and medications can be expensive, and planning around payment can be stressful. A study from 2007 suggested that the “cost of illness” for a person with ADHD is $14,576 each year. That means ADHD costs Americans $42.5 billion dollars each year — and that’s on the conservative side of ADHD prevalence estimates.

Medicines and treatments aren’t the only costs to consider when dealing with an ADHD diagnosis. Other factors that can add cost include:

Boys and girls can display very different ADHD symptoms, and boys are much more likely to be diagnosed with the attention disorder. Why? It’s possible the nature of ADHD symptoms in boys makes their condition more noticeable than it is in girls.

Boys tend to display externalized symptoms that most people think of when they think of ADHD behavior, for example:

impulsivity or “acting out”

hyperactivity, such as running and jumping

lack of focus, including inattentiveness

ADHD in girls is often easy to overlook because it’s not “typical” ADHD behavior. The symptoms aren’t as obvious as they are in boys. They can include:

being withdrawn

low self-esteem and anxiety

impairment in attention that may lead to difficulty with academic achievement